Epidemiology

Incubation period days

Incubation Cycle

Period of communicability Bugs become infected after 8-10 days and remain so for life, which lasts about 2 years. Infected persons have circulating trypanosomes in the acute and early chronic stages of the disease, Fig. 15.18. Different forms of the trypanosomidae. and this may persist in small numbers for the life of the individual. Occurrence and distribution Chagas' disease is found throughout Central America and in most countries of South America. Considerable progress has been made in...

Transmission

Scrub typhus Like wild rodent plague, scrub typhus is a zoonosis in which humans are not involved. Well-defined areas, called mite islands, harbour rodents, mites and the Orientia, which is transmitted between them. A large number of rodents have been incriminated, including rats, and it is their system of burrows, runs and range of activity that determines the limit of the mite island. The rodents are fed upon by the larval stage of various Leptotrombiculid mites that need to take blood so...

BCG vaccination

Functions Rntcp

Vaccination by BCG induces cell-mediated immunity to the mycobacteria and does not generate humoral immunity, as do other vaccines. BCG vaccination, therefore, alerts the body's defences rather than inducing antibody formation. After a BCG vaccination a primary infection will still take place, but the progressive or disseminated infection will be reduced. Effectiveness of BCG varies considerably in different countries - in Europe, there is a good response, while in India, it is marginal. This...

Leishmaniasis

Epidemiology Leishmania Donovani

There are seven species of Leishmania and a number of subspecies leishmaniasis (donovani, infantum, chagasi, archibaldi) L. braziliensis (braziliensis, peruviana), L. guyanensis (guyanensis, panamensis) L. mexicana (mexicana, amazonensis, pifanoi, garnhami, venezuelensis) L. major Old world cutaneous Old world cutaneous They are all transmitted by the bite of the sandfly and undergo the same simple life cycle. Promastigotes enter man with the bite of the sandfly, change into...

Vaccine schedules

The type of vaccine and the age of risk of developing the target disease determine the optimum time and schedule for administering each vaccine. The characteristics of the principal vaccine-preventable diseases (included in the Expanded Programme of Immunization (EPI) programme in most developing countries) are as follows Tetanus can enter the neonate through an infected umbilical cord, producing a high mortality. Protection is by immunizing pregnant women with tetanus toxoid. This protection...

Hepatitis E HEV

Organism An enteric (E) virus provisionally classified as a calicivirus. Clinical features Hepatitis E is very similar to hepatitis A except that it nearly always occurs in large epidemics. The main difference is that hepatitis E results in a high mortality in pregnant women (up to 20 ). Transmission Similar to hepatitis A, although the main means of transmission is via water. A reservoir has been found in wild and domestic pigs, suggesting a zoono-tic pattern of transmission. Diagnosis is by...

Chickenpox Shingles Varicella

Organism Herpesvirus varicella-zoster virus (VZV). Clinical features A generally mild disease, chickenpox is a common infection of children. Illness commences with fever followed by a characteristic skin rash of macules, papules, vesicles, pustules and dried crusts. The lesions occur in groups, appearing over several days, so pox of different stages will be seen at the same time. In chickenpox, the rash is distributed centrally, appearing on the chest and abdomen and sparsely on the feet and...

Hepatitis B HBV

Clinical features In many parts of the developing world, HBV infection is common, but only about 30 show any symptoms. However, these symptomatic cases present as a more severe disease than hepatitis A, with a persistent jaundice, often resulting in liver damage. After an insidious onset with anorexia, nausea and abdominal discomfort, jaundice then develops, from which the patient either recovers or goes on to develop chronic active disease. Low-grade infection continues with periods of...

Hepatitis C HCV

Clinical features Similar in many respects to hepatitis B, HCV produces a milder disease, but as many as 10-20 will progress to cirrhosis and 1 to liver cancer in later life. Diagnosis is difficult, dependent upon detecting antibodies to HCV and confirming by a recombinant immunoblot assay (RIBA). PCR is now commonly used. Transmission is due to the use of poorly sterilized needles, giving-sets and other methods of parental administration and so is common in developing countries and in those...

Lymphatic Filariasis

Distribution Onchocerciasis

Organism Wuchereria bancrofti, Brugia malayi and B. timori, nematode worms. Microfilariae, the larval form present in the peripheral blood, are taken into the mosquito's stomach when it feeds on humans or animal reservoir in B. malayi . The larva loses its sheath inside the mosquito, migrates through the stomach wall and burrows into the muscles of the thorax. It becomes shorter and fatter, commonly described as sausage-shaped. Developmental changes take place and it elongates to a third stage...

Force of Infection

In a communicable disease, the number of new cases occurring in a period of time is dependent on the number of infectious persons within a susceptible population and the degree of contact between them. Persons, whether infectious or susceptible, and a period of time are all quantifiable factors, but the degree of contact can depend upon very many variables some of which have been covered above . The factors, such as proximity density of populations, carriers, reservoirs, climate and...

Yaws Epidemiology

Organism Treponema pallidum subspecies pertenue. Clinical features Yaws is a non-venereal treponemal disease affecting both the skin and bone. It commences as a primary papule that starts to heal, but after a period, varying from a few weeks to several months, it is followed by generalized lesions, multiple rounded papules, scattered all over the body. These lesions exude serum, which is highly infectious. There is also a mild periostitis in focal bony sites, but these and the skin lesions...

Protection of foods

Excreta Borne Dsease

Food-transmitted infections can spread either through contamination or by a specific intermediate host. Flies indirectly contaminate food. Protection of the food we eat can be by the following Fig. 3.4. Routes of transmission of the water- and sanitation-related diseases. Fig. 3.4. Routes of transmission of the water- and sanitation-related diseases. Table 3.1. A classification of water- and excreta-related diseases. Table 3.1. A classification of water- and excreta-related diseases. Modified...

Incubation period months

Heterophyes Heterophyes Epidemiology

Period of communicability is 12 months, but animals act as a permanent reservoir. Occurrence and distribution East Asia, especially China, Taiwan, Thailand, Borneo and Malaysia, in some 15 million people. Control and prevention is by the proper preparation and cooking of water plants. Much can be done to reduce transmission by regulating the use of human faeces as a fertilizer. Domestic animals should be kept away from water plant cultivation ponds. Fig. 9.1. Parasite eggs found in faeces,...

The Fishtransmitted Liver Flukes

Heterophyes Heterophyes Epidemiology

Organism The trematode fluke Opisthorchis sinensis previously called Clonorchis . Clinical features The adult fluke lives in the branches of the bile duct resulting in trauma and inflammation. Dilation of the biliary system causes a distortion of the liver architecture, which can lead to biliary stasis, hepatic engorgement, fatty infiltration and finally cirrhosis. O. sinensis is a risk factor for cholangiocarcinoma. Migration of the flukes up the pancreatic duct can damage the pancreas leading...

HIV infection

Nyc Epidemiological Causes Hiv

occupations or environments that damage the lung (mining, dust, smoke). As well as variation amongst individuals, there are also considerable differences in the susceptibility of populations. This can be measured by the annual tuberculosis infection rate, which compares the tuberculin reaction of non-vaccinated subjects of the same age every 5 years. With BCG vaccination at birth, this cannot be done any longer, but data obtained before this became a universal policy is still valid. Another...

Hard ticks Ixodidae

Hyalomma Lus

Hard ticks are responsible for transmission of several different kinds of organisms including rickettsiae, Borrelia and arbo-viruses. The genera of medical importance are Amblyomma, Dermacentor, Haemaphy-salis, Hyalomma, Ixodes and Rhipicepha-lus. A female Dermacentor, to characterize the group of hard ticks, is illustrated in Fig. 16.5. The feature that distinguishes hard from soft ticks is the presence of a scutum shield and protruding mouthparts. Care has to be taken in identifying the...

Population size

Basic Reproductive Rate

As mentioned above, the continuation of an epidemic is determined by the number of susceptibles remaining in the population. Fig. 2.6. Basic reproductive rate increasing - i.e. gt 1. Maximal transmission every infection produces a new case. Fig. 2.6. Basic reproductive rate increasing - i.e. gt 1. Maximal transmission every infection produces a new case. Fig. 2.7. Basic reproductive rate decreasing- i.e. lt 1. Unsustained transmission each transmission gives rise to less than one new case and...

Onchocerciasis

Lalat Simulium Vector Filariasis

Organism Onchocerca volvulus, a nematode worm that has a predilection for the skin and eye, is transmitted by Simulium flies. Microfilariae are taken up by the fly when it bites humans and then undergo larval changes within the thoracic muscles, migrating to the head of the fly as infective larvae. When the fly bites again, microfilar-iae break out on to the skin to enter via any abrasion, especially the bite wound. Clinical features The microfilariae as they migrate through the skin cause...

The physical environment

Topography The nature of the physical surroundings can influence the diseases that are found there. In much of Asia, a complex interaction termed 'forest fringe malaria' describes the greater likelihood of developing malaria at the forest margin. The man enters the forest to fell timber, often illegally, while the woman goes there to collect firewood, bringing them into range of mosquitoes that live within the forest cover. A similar cycle of transmission occurs with yellow fever as illustrated...

Rhodesiense sleeping sickness

Imagenes Del Rhodesiense

The principal vector of T. b. rhodesiense is G. morsitans, which breeds along water courses, but then travels widely throughout the extensive shade cover provided by the forest belt. This open type of forest, commonly called miombo (mainly Brachystegia and Julbemardi spp.), is found in large areas of East Africa. Smaller wild animals inhabit it, especially the bushbuck that forms a reservoir of infection. Towards the margins of this forest belt, it breaks up into thickets separated by savannah...

No meningitisx Relative humidity

The seasonal variation of meningococcal meningitis in relation to relative humidity in the Sahel region of Africa. the northern boundary is the desert. Within this area, major epidemics, mainly of group A, occur at 7-14-year intervals, with lesser ones in between. In addition to the meningitis epidemic belt in Africa, there have also been epidemics of group A organisms in India and Nepal, and group B in the Americas, Europe and Pacific Island Nations. Epidemic meningitis is commonest...

Acute Rheumatic Fever

Organism Group A p-haemolytic streptococcus (GApHS). The M-protein in the wall of the streptococcus is responsible for its virulence and certain predominant sero-types, 1, 3, 5, 6, 14, 18, 19, 24, 27 and 29, have a much greater rheumatogenic potential. Clinical features ARF is a delayed non-sup-purative sequel of upper respiratory tract infection or scarlet fever with GApHS. ARF is important because it can lead to rheumatic heart disease (RHD), the resulting cardiac damage producing...

Hydatid Disease

Turkana Hydatid

Organism Echinococcus granulosus, a cyclophyllidean tapeworm of canines. Clinical features Hydatid cysts, the intermediate stage of the parasite, have been recorded from all parts of the human body. The commonest site is the liver, with lung, abdomen, kidney and brain in descending order of frequency. As the cysts increase in size, they can cause serious problems some times fatally. The cyst contents are infective so if it ruptures either accidentally or at operation, then numerous new cysts...

Poliomyelitis Polio

Organism Poliovirus (Enterovirus) types 1, 2 and 3. Clinical features Infection commences with fever, general malaise and headache, the majority of cases resolving after these mild symptoms, but approximately 1 proceed to paralytic disease. The virus has a predilection for nerve cells, especially those with a motor function (the anterior horn cells of the spinal cord and the motor nuclei of the cranial nerves). These cells are destroyed and a flaccid paralysis results. As a generalization,...

Hepatitis Delta HDV

Organism Hepatitis delta virus HDV is dependent on HBV infection of the person. Either both viruses can infect at the same time or HDV infects an already infected HBV carrier. Clinical features With coinfection both viruses infecting at the same time , there is normally a self-limiting infection with only about 5 continuing into the chronic form of HDV. However, with superinfection HDV infection of an already HBV-infected person , there is a severe acute hepatitis with 80 continuing to chronic...

Table The vectors and reservoirs of leishmaniasis

Visceral L. donovani including infantile Mucocutaneous L. braziliensis L. guyanensis L. mexicana Mexico, Belize, Guatemala Phlebotamus peniciosus, P. ariasi, P. major syriacus, P. longicuspis P. major syriacus, P. smirnovi, P. longiductus P. chinensis P. argentipes, P. papatasi P. orientalis, P. martini P. papatasi P. papatasi, P. P. papatasi P. sergenti P. duboscqi P. longpipes P. pedifer Rodents, dogs, gerbils Dogs, rodents Rodents, gerbils Dogs The global distribution of cutaneous and...

Tickborne Relapsing Fever

Picture Soft Tick

Organism Borrelia dutoni, which is indistinguishable from B. recurrentis in stained blood films. Clinical features Fever develops with a recurring or relapsing pattern as the name of the disease indicates. The period of fever lasts for a few days and then recurs after 2-5 days, with up to ten or more relapses occurring in the untreated case. The onset of fever is sudden with headache, myalgia and vertigo a transient petechial rash can occur and a variety of other systems may be involved. There...

Leptospirosis

Organism Leptospira interrogans with a large number of serovars, the most important of which is icterohaemorrhagiae. It is passed in rat's urine and can contaminate any area that they frequent. For the survival of the organism, there must be moisture, such as a canal or sewer, or else in damp soil, the washings of abattoirs or similar conditions. The pH of the soil or water is important and the Leptospira cannot survive in an acid environment. Leptospirosis is, therefore, commoner in places...

Classification of Communicable Diseases

No biological system is perfect and communicable diseases in particular are not readily classified however, any grouping makes it easier to understand and remember, so the objective of this short chapter is to look at the different ways this can be done. A disease is a morbid condition of the body (e.g. measles or plague). As the cause of diseases were discovered, they became identified by the causative organism, such as trypanosomiasis or pneumococcal meningitis, but confusion arose because...

Domestic and Synanthropic Zoonoses

A zoonosis is an infection that is naturally transmitted between vertebrate animals and humans. In the last chapter, a group of infections that were mainly zoonoses, but also involved a vector were covered, while this chapter includes infections in which a vector is not involved. Most of these infections are due to the close association humans have with their domestic animals, but there are also some zoonoses in which animals that live close to humans, but are not welcomed, such as rats, are...

Incubation period weeks

Period of communicability is while open lesions are present, which can be for a considerable period of time in the untreated patient. Occurrence and distribution Mainly in the tropical regions of the world, especially in southern India and Irian Jaya Papua New Guinea and amongst the aboriginal people of Australia. It is less commonly found in Africa and people of African origin, such as in the Caribbean and the northern part of South America. It is a disease of the sexually active 20-40-year...

The Beef and Pork Tapeworms

Organism Taenia saginata, the beef tapeworm and T. solium the pork tapeworm. Clinical features The adult worm of both species can live in the intestines producing little pathology, being diagnosed often by accident. It does, however, share the food supply of its host so that when intake is inadequate, debility can occur. The serious problems are due to the Cysticercus cellulo-sae from T. solium . The cysts die and calcify, those in the brain being a common cause of epilepsy or mental disorder....

Nongonococcal Urethritis NGU

Organism A number of organisms have been found to be responsible for urethritis not caused by the gonococcus, including Chlamydia trachomatis, Ureaplasma urea-lyticum, Trichomonas vaginalis and Mycoplasma hominis. Clinical features A low-grade urethritis with mucoid rather than purulent discharge in the male, in which intracellular diplococci are not found in the smear, suggests NGU. Infection is a low-grade discharge in the female or is often asymptomatic so that a reservoir of infection can...

Human Papilloma Virus HPV

Clinical features The main clinical presentation is genital warts on the external genitalia or within the vagina, but a large proportion of infected persons show no clinical signs. When cellular immunity is depressed condylomata acuminata, large fleshy growths in moist areas of the perineum develop. However, the most serious consequence of HPV infection is the development of carcinoma, particularly of the cervix, but the anus and penis can also be involved....

Meningococcal Meningitis

Many ser-ogroups and sub-groups have been identified, but of these A, B, C and Y are the most important in producing disease, while A and C predominate in epidemics. W135 has recently been responsible for some outbreaks. Clinical features Fever, headache, vomiting, neck stiffness and progressive loss of consciousness. A petechial rash, which does not blanch, is an important sign. Infants show floppiness and high-pitched crying, while children may present with...

Investigation of propagated source epidemics

Propagated Source Epidemic

With a propagated source epidemic, phases of infection occur at regular intervals. The time-period between these phases is called the serial interval Fig. 2.5 . Features of the epidemic are measured in the same way as a common source epidemic, while an estimate of time of recurrence is given by the serial interval. After several propagated epidemics, cases remaining from the previous epidemic will merge with the next so that the regular serial pattern will be lost. Contagiousness or the...

Cryptosporidiosis

Organism Cryptosporidium parvum is a protozoan parasite found in poultry, fish, reptiles and mammals, especially cattle, pigs, sheep, dogs and cats, from which the infection can be acquired. Clinical features Cryptosporidiosis presents as an acute watery diarrhoea associated with abdominal pain. Fever, anorexia, nausea and vomiting can also occur, especially in children. There may be repeat attacks, but these do not normally continue for more than a month. In the immunodefi-cient, especially...

Insecticides

Ectoparasites favour dirty dark places, whether they are searching for a suitable habitat on a person or a vantage place in the house from which to mount an attack. Fleas and lice are not removed by washing, but the continued use of warm water and soap considerably deters them. If this is combined with washing of clothes, then fleas can rapidly be controlled. Where possible, clothes and bedding should be boiled or at least subjected to very hot water as fleas are not affected by cold water....

The Lung Fluke

Organism Unique amongst all the helminths, the trematode Paragonimus wester-mani selectively inhabits the lung. Clinical features Foreign body reaction to the parasite in the lung results in fibrosis, compensatory dilation and abscess formation. Haemoptysis is often an important feature, mimicking tuberculosis. Symptoms include cough and chest pain. If the parasite migrates to a site other than the lung, it can cause CNS, liver, intestinal, genitourinary or subcutaneous disease. Diagnosis is by...

Food poisoning due to bacteria

Organism Food poisoning can either be due to bacteria, viruses, organic or inorganic poisons Table 9.1 . The most common poisoning is that produced by bacteria. The main types of bacterial food poisoning are due to Salmonella, Staphylococcus or Clostridia. Clinical features Due to the similarity of presentation, it is more convenient to consider them as a group, rather than individually. Onset is sudden with fever, generally vomiting and or diarrhoea in a family or group of persons who have...

Acute Respiratory Infections ARI

The acute respiratory infections (ARI) are the commonest causes of ill health in the world. WHO have estimated that there are 14-15 million deaths a year in children under 5 years of age and one-third of these are due to ARI, yet despite their importance, they are a poorly defined group of diseases. They include the common cold, influenza, pneumonia, bronchitis and a number of other infections. They can be separated by clinical criteria, but it is the differing response of the individual to the...

Fish poisoning

Organism Fish poisoning is a specific form of food poisoning caused by toxins present in the fish or shellfish when they are caught or which develop due to partial decomposition taking place if they are not eaten straight away or refrigerated. Ciguatera toxin is produced by the dinoflagellate Gam-bierdiscus toxicus, which is present in algal blooms, often called red tides, while shellfish poisoning can de due to the dino-flagellates Gonyaulux, Gymnodinium, Dinophysis or Alexandrium. Clinical...

Nonspecific tropical ulcers

Organism No specific organism is normally detected, but initial infection is often accompanied by cellulitis, probably caused by a Streptococcus. Transmission Flies are responsible for contaminating small wounds and scratches or occasionally biting insects transmit infecting organisms directly. Scratching of the wound by the host can be a potent method of instilling organisms into the skin. Clinical features The initial wound becomes red and indurated, with cellulitis spreading to the regional...

Treatment and Mass Drug Administration

Treatment of the sick is not only a humanitarian action, but reduces the length of illness and, therefore, the period of commu-nicability, thereby aiding control. However, where treatment is incomplete, it can actually prolong the period of communicability, encourage the development of carriers or worst of all, resistant organisms. Case finding and treatment is the main method of control for leprosy Section 12.6 and tuberculosis Section 13.1 , but careful follow-up is essential to ensure that...

Climate change due to global warming

The increase in carbon dioxide and other pollutants in the atmosphere due to the burning of fossil fuels coal, petrol, etc. has led to an increase in global temperature. Although the temperature increase is comparatively small, it has begun to have a major effect on the climate, with a disruption of weather systems and a raising of the sea level. This has been most marked on a system of currents off the west coast of South America known as the El Nino southern oscillation. Climatic systems are...

The Sheep Liver Fluke Fasciola hepatica

Organism The sheep liver fluke Fasciola hepatica. Less commonly F. gigantica. Clinical features The parasite has a predilection for the liver, piercing the gut wall and migrating through the liver substance to lie in the biliary passages. This migration and residence in the liver causes extensive damage, leading to fibrosis and cirrhosis. Diagnosis is made by finding the very large egg in the stool, which is almost identical to that of Fasciolopsis Fig. 9.1 . Transmission The life cycle is...

Excreted load and infective dose

The number of organisms excreted can vary considerably due to the type of infection or the stage of the disease. In diseases such as cholera, there may be vast numbers of organisms excreted (106-1012 vibrios g of faeces), whereas in hookworm infection, the number of eggs may be comparatively few. In Schistosoma mansoni, asymptomatic children excrete the largest number of eggs, whereas the adult exhibiting severe manifestations may be almost non-infectious. In the otherwise harmless typhoid...

Faecal Oral Diseases

The faecal-oral group of diseases is transmitted by person-to-person contact, through water, food or directly to the mouth. The absence of a proper water supply, rubbish and dirty surroundings with an abundance of flies are the typical situations in which these diseases thrive. The incidence of these diseases can be controlled by (i) breaking the faecal-oral cycle with personal hygiene (ii) increase in water quantity (iii) improvement in water quality (iv) food hygiene and (v) the provision of...

Gastroenteritis

Gastroenteritis is a common form of diarrhoea that predominantly attacks children. It is endemic in developing countries, but seasonal epidemics occur. Attempts to find a specific organism as a cause are often unsuccessful and not essential, as management and control are the same. Strains of enterotoxigenic, enteropathogenic and enteroag-gregative Escherichia coli as well as enteric viruses, particularly rotavirus, are the main organisms. Campylobacter (Section 9.2) is now a major cause....

Routine or passive surveillance

All health facilities collect data in their record keeping, at its simplest being the name, age and sex of the individual and the symptoms or diagnosis of their illness. Considerable use can be made of well-kept records and it is worth doing an analysis of the type of information collected to determine the best system to use with the resources available. Hospital records, while more detailed than in small clinics, will not be representative of the population. Additional categories can be added...

Susceptibility

Genetic Certain diseases can only affect animals and when they are transmitted to man, they are not able to establish themselves. An example is Plasmodium berghei, the rodent malaria parasite, which cannot produce disease in man although closely related to the human malaria parasite. However, some newly emergent diseases have succeeded in crossing this genetic barrier, such as HIV and severe acute respiratory syndrome (SARS). Genetic disposition also determines the host's response to infecting...

Ebola Haemorrhagic Fever

Organism Virus of the Filoviridae group of organisms. Clinical features Illness presents with sudden onset of fever, headache, muscle pains, sore throat and profound weakness. This progresses to vomiting, diarrhoea and signs of internal and external bleeding, generally with the occurrence of liver and kidney damage. Mortality is 50-90 . Diagnosis is by ELISA for specific IgG and IgM antibody or by PCR, but should only be carried out in laboratories with maximum facilities for protecting staff....

Lassa Fever

Organism Lassavirus is an arenavirus. Clinical features There is a gradual onset with fever, malaise, sore throat, cough, vomiting, diarrhoea and general aches and pains. By the second week, lymphadenop-athy, pharyngitis and a maculo-papular rash on the face or body develops. In severe cases, pleural effusion, encephalopathy, cardiac and renal failures can occur with a mortality of 15-20 . In endemic areas, 80 of cases are mild or asymptomatic so that serological investigation will find a large...

Epidemic Theory

Epidemics can occur unexpectedly, as when a new disease enters a community, or can occur regularly at certain times of the year, as in epidemics of measles. Epidemic contrasts with endemic, which means the continuous presence of an infection in the community and is described by incidence and prevalence measurements. This section will cover epidemics and how they are measured. Epidemic means an excess of cases in the community from that normally expected, or the appearance of a new infection....

Hepatitis A HAV

Organism Infectious hepatitis is a viral infection caused by a member of the Picorna-viridae, which includes both enteroviruses and rhinoviruses. Clinical features The main pathology is inflammation, infiltration and necrosis of the liver, resulting in biliary stasis and jaundice. The infection generally starts insidiously, the person feels lethargic, anorexic and depressed. Fever, vomiting, diarrhoea and abdominal discomfort ensue before the appearance of jaundice reveals the diagnosis. Once...

African Trypanosomiasis Sleeping Sickness

Organism There are two forms of human sleeping sickness in Africa - one due to Trypanosoma brucei gambiense and the other caused by T. b. rhodesiense. A third form T. b. brucei is found in cattle, causing considerable economic loss. The trypanosome exists in several different forms during its life cycle (Fig. 15.18). When seen in human blood, the trypomasti-gotes are long and slender, short and stumpy, or intermediate between the two, probably representing a cycle of antigenic variation (Fig....

Western equine Eastern equine St Louis Venezuelan Japanese Murray Valley and Rocio

This group of diseases present with a high fever of acute onset, headache, meningeal Table 15.1. The important arbovirus infections of humans. Onyong-nyong West Nile Oropuche Orungo Ross River Australia, New Zealand, Pacific Islands Aedes aegypti, Ae. africanus, Ae. leuteocephalus Anopheles gambiae, A. modestus, C. univittatus Mosquitoes, possibly Culicoides Ae. dentatus, Anopheles spp. C. annulirostris, Ae. vigilax, Ae. polynesiensis Western Equine Americas Eastern Equine Americas, Caribbean...

Trichinosis

Organism Trichinella spiralis Fig. 9.7 , T. nelsoni, T. nativa, T. britovi and T. pseu-dospiralis, nematode worms. Clinical features The severity of the disease depends upon the dose of larvae that have encysted in the tissues. During the second week of infection, there is headache, insomnia, pain, dyspnoea and pyrexia with oedema of the orbit and eosinophilia. If the symptoms are sufficiently severe, death can result otherwise, once the attack is over, the cysts cause no further trouble,...

The cold chain

The cold chain is a descriptive term for the whole sequence of links that must be maintained in transporting the vaccine in a viable condition from the manufacturer to the person to be vaccinated. Vaccines will only survive when they are maintained at the correct temperature. There are certain limits when the vaccine can be allowed to depart from the optimal temperature, but the range and time are very short and vaccines rapidly lose their potency. To vaccinate with nonpotent vaccine is not...

Investigation of a common source epidemic

In the investigation of any outbreak of a disease, the basic approach is to gather information on the following 1. Persons age, sex, occupation, ethnic group, etc. comparing the number infected with the population at risk. 2. Place country, district, town, village, household and relationship to geographical features such as roads, rivers, forests, etc. conveniently marked on a map. 3. Time annual, monthly seasonal , daily and hourly nocturnal diurnal . The number of cases occurring within each...

Mobile and static clinics

Vaccination can be from static and or mobile clinics. Their various advantages and disadvantages are given in the following table A static clinic responsible for providing primary care services including delivery for both the mother and the child is the most effective. A child stands a greater chance of receiving all its vaccines from a static health unit. However, as distance from the clinic increases, the probability of a mother bringing her child to the clinic decreases for every kilometer...

Bacillary Dysentery Shigellosis

Organism Bacillary dysentery is due to Shigella invading the bowel. The species and strains of Shigella are numerous. There are four main groups S. dysenteriae with 12 serotypes S. flexneri with 14 serotypes S. boydi with 18 serotypes S. sonnei with one serotype. The most severe are S. dysenteriae and the least severe S. sonnei, with S. flexneri being the most common in endemic areas. Another form of bloody diarrhoea is due to enteroinvasive and enterohaemorrhagic E. coli, particularly serotype...

The Intestinal Fluke Fasciolopsis

Organism The large human fluke Fasciolop-sis buski. Clinical features The adult worm lives in the small intestines and produces damage by inflammatory reaction at the site of attach ment. This sometimes leads to abscess and haemorrhage, but as well as these local effects, the parasite produces toxins. These can lead to oedema, weakness and prostration, ending fatally in the debilitated child. Diagnosis is made by finding the egg in faeces, a giant among parasites Fig. 9.1 . The egg is...

Control and prevention is by use of pit

Latrines or other methods of sanitation. The wearing of footwear effectively prevents penetration by the larvae. The open sandal type of footwear often worn (thongs, flipflops) is not effective and infection can readily occur. Mass treatment can be given to reduce the parasite load, but without health education and the proper use of latrines, it will only produce a temporary improvement. Treatment A number of drugs are effective in treatment. Albendazole 400 mg single dose, mebendazole 500 mg...

Period of communicability years

Occurrence and distribution S. haemato-bium and S. mansoni were originally diseases of Africa, where they are widely distributed, but with the massive exodus of slaves that took place in the 17th and 18th centuries, this legacy was carried with them. The East African slave trade carried S. mansoni to the Arabian peninsula and S. haematobium to the Yemen and Iraq. The Western trade was solely in S. mansoni, which found a suitable snail host in South America and the Caribbean. S. japonicum...

Gambian sleeping sickness

Sleeping sickness as with other vector-borne diseases is determined by the habits of the vector. In the gambiense type, the tsetse fly breeds in the tunnel of the forest, along the course of rivers (Fig. 15.17). Although powerful flyers, they do not range far from this shaded protection, but travel extensively through this tunnel of forest in search of blood meals. Any mammals, including humans, that come to the river to drink or cross are attacked and fed upon. Humans are the main reservoir of...

Control and prevention

Knowledge of the habits and behaviour of the local vector is necessary before embarking on methods of vector control. The principal method is to modify the environment so that it is unsuitable for the fly, but not to cause so much damage that the water table is affected or soil erosion results. With the riverine type of habitat, areas of the forest tunnel are cleared removing all the dense undergrowth, but leaving the big trees with their extensive root systems to prevent...

American Trypanosomiasis Chagas Disease

The trypano-some in American trypanosomiasis undergoes a development cycle both in the vector bug and the vertebrate host, with trypomastigotes, the infective form and pseudocysts forming in the muscle. These contain amastigotes, which grow a flagellum to become promastigotes and epimastigotes (Fig. 15.18) when the pseudocyst ruptures, finally developing into infective trypomas-tigotes (Fig. 15.19). The trypomastigote of the American disease has a larger kineto-plast...