C. N. L. Macpherson

The socioeconomic burden of parasitic zoonoses: global trends.

Diseases resulting from zoonotic transmission of parasites are common. Humans become infected through food, water, soil and close contact with animals. Most parasitic zoonoses are neglected diseases despite causing a considerable global burden of ill health in humans and having a substantial financial burden on livestock industries. This review aims to bring together the current data available on global burden estimates of parasitic zoonoses and indicate any changes in the trends of these diseases. There is a clear need of such information as interventions to control zoonoses are often in their animal hosts. The costs of such interventions together with animal health issues will drive the cost effectiveness of intervention strategies. What is apparent is that collectively, parasitic zoonoses probably have a similar human disease burden to any one of the big three human infectious diseases: malaria, tuberculosis or HIV in addition to animal health burden. Although the global burden for most parasitic zoonoses is not yet known, the major contributors to the global burden of parasitic zoonoses are toxoplasmosis, food borne trematode infections, cysticercosis, echinococcosis, leishmaniosis and zoonotic schistosomosis. In addition, diarrhoea resulting from zoonotic protozoa may have a significant impact.

The epidemiology and public health importance of toxocariasis: a zoonosis of global importance.

Toxocariasis, caused by infection with larvae of Toxocara canis, and to a lesser extent by Toxocara cati and other ascaridoid species, manifests in humans in a range of clinical syndromes. These include visceral and ocular larva migrans, neurotoxocariasis and covert or common toxocariasis. Toxocara canis is one of the most widespread public health and economically important zoonotic parasitic infections humans share with dogs, cats and wild canids, particularly foxes. This neglected disease has been shown through seroprevalence studies to be especially prevalent among children from socio-economically disadvantaged populations both in the tropics and sub-tropics and in industrialised nations. Human infection occurs by the accidental ingestion of embryonated eggs or larvae from a range of wild and domestic paratenic hosts. Most infections remain asymptomatic. Clinically overt infections may go undiagnosed, as diagnostic tests are expensive and can require serological, molecular and/or imaging tests, which may not be affordable or available. Treatment in humans varies according to symptoms and location of the larvae. Anthelmintics, including albendazole, thiabendazole and mebendazole may be given together with anti-inflammatory corticosteroids. The development of molecular tools should lead to new and improved strategies for the treatment, diagnosis and control of toxocariasis and the role of other ascaridoid species in the epidemiology of Toxocara spp. Molecular technologies may also help to reveal the public health importance of T. canis, providing new evidence to support the implementation of national control initiatives which have yet to be developed for Toxocara spp. A number of countries have implemented reproductive control programs in owned and stray dogs to reduce the number of young dogs in the population. These programs would positively impact upon T. canis transmission since the parasite is most fecund and prevalent in puppies. Other control measures for T. canis include the regular and frequent anthelmintic treatment of dogs and cats, starting at an early age, education and enforcement of laws for the disposal of canine faeces, dog legislation and personal hygiene. The existence of wild definitive and paratenic hosts complicates the control of T. canis. Increasing human and dog populations, population movements and climate change will all serve to increase the importance of this zoonosis. This review examines the transmission, diagnosis and clinical syndromes of toxocariasis, its public health importance, epidemiology, control and current research needs.

A large focus of alveolar echinococcosis in central China

Human alveolar echinococcosis (AE) is a rare and highly pathogenic helminthic zoonosis due to infection with the intermediate stage of the small fox tapeworm, Echinococcus multilocularis. Parasite transmission is restricted to northern latitudes, including central and north China, from where few clinical and no detailed community studies have been reported. In August, 1991, 65 (5%) of 1312 people residing in three rural communes of Zhang County, Gansu Province, China were diagnosed as having hepatic AE after mass ultrasound scanning with serological back-up. This represents one of the highest prevalence rates of AE ever recorded. It is also the first time that mass ultrasound scanning and serology have been used together in an AE endemic region. The region was selected one year earlier, when a preliminary serosurvey on 606 unselected people in the same locality resulted in an 8.8% serum antibody positive rate with a 76% rate of confirmation of hepatic AE in 37 individuals who could be followed up in 1991. Seropositivity rates varied for villages between 0 and 20.5%. Overall, females (7.8%) had a significantly greater risk of infection than males (2.5%), especially in the 31-50 age group, a difference which may be related to contact with dogs and dog faeces over many years. Age-specific prevalence of AE increased from 0% in the under 5-year group to 8.2% in those aged 31-50. The youngest case was 11 years and the mean age of diagnosis was 40 years. Adult tapeworms of E multilocularis were identified from the small intestines of 10% of domestic dogs. Sylvatic animal hosts of the parasite have not yet been identified. The high prevalence of human AE in this region of central China is most probably due to semi-domestic transmission of E multilocularis between wild rodents and dogs, together with the poverty and poor hygiene in these rural communities.

Dogs, zoonoses and public health.

Zoonotic diseases constitute a public health problem throughout the world. Addressing a little studied area of veterinary and medical science, this book covers the viruses, bacteria and protozoan and helminth parasites that are transmitted between man and dogs, discussing population management, control disease agents and human-dog relationships. Fully updated throughout, this new edition also includes two new chapters on benefits of the human-dog relationship and non-infectious disease issues with dogs. It is a valuable resource for researchers and students of veterinary and human medicine, microbiology, parasitology and public health.

Application of ultrasound in diagnosis, treatment, epidemiology, public health and control of Echinococcus granulosus and E. multilocularis

The last 30 years have seen an impressive use of ultrasonography (US) in many fields of veterinary and clinical medicine and the technique is being increasingly applied to a wide variety of parasitic infections including the cestode zoonoses Echinococcus granulosus and E. multilocularis. US provides real-time results which are permanently recordable with a high resolution and diagnostic accuracy. These properties, coupled with the clinical value of the images obtained and the non-invasive nature of the test which is safe, require no special patient preparation time; it is easy to operate and this has resulted in the establishment of US as the diagnostic technique of choice for cystic (CE) and alveolar (AE) echinococcosis. The lack of ionizing radiation and side-effects mean that examination times are not restricted. The hand-held probes facilitate what amounts to a rapid, bloodless non-invasive laparotomy, enabling a search from an infinite number of angles for lesions producing information on their number, size and type of cysts, their location and clinical implications. Such clinical information has facilitated the development of treatment protocols for different cyst types. Less invasive surgical techniques, such as US guidance for PAIR (Puncture, Aspiration, Injection, Re-aspiration), PAIRD (PAIR plus Drainage) or PPDC (Percutaneous Puncture with Drainage and Curettage) are also possible. Longitudinal US studies have facilitated monitoring the effects of the outcome of treatment and chemotherapy. Portable ultrasound scanners which today weigh as little as a few pounds, powered by battery or generators have facilitated the use of the technique in mass community-based screening studies. The majority of these studies have been conducted in remote, low socio-economic areas where there were few, if any, hospitals, veterinary facilities, schools or trained personnel. The surveys led to the discovery of unexpectedly high prevalences of CE and AE in asymptomatic individuals of endemic areas and especially amongst transhumant or nomadic pastoralists living in various parts of the world. Screening for CE and AE is justified as an early diagnosis leads to a better prognosis following treatment. The application of US in field and clinical settings has led to a better understanding of the natural history of CE and AE and to the development of a WHO standardized classification of cyst types for CE. This classification can be used in helping define the treatment options for the different cysts found during the surveys, which in turn can also be used to calculate the public health cost of treating the disease in an endemic community. The case mix revealed can also influence the specificity (particularly proportions of cyst types CE4 and CE5 and cystic lesions--CL) of US as a diagnostic test in a particular setting. Community based US surveys have provided new insights into the public health importance of CE and AE in different endemic settings. By screening whole populations they disclose the true extent of the disease and reveal particular age and sex risk factors. Through the treatment and follow-up of all infected cases found during the mass screening surveys a drastic reduction in the public health impact of the disease in endemic communities can be achieved. Educational impacts of such surveys at the national, community and individual levels for both professional and lay people are beginning to be appreciated. The translation of the information gained into active control programmes remains to be realized. In areas where intermediate hosts, such as sheep and goats, are not slaughtered in large numbers mass US screening surveys to determine the prevalence of CE in livestock has proved possible. Longitudinal studies in such intermediate hosts would reveal changes in prevalence over time, which has been used as a marker for control success in other programmes. Mass US screening surveys in an ongoing control programme in Argentina has demonstrated the early impact of control in the human population and identified breakthroughs in that control programme. Mass US screening surveys must adhere to the highest ethical standards and the outcome of surveys should result in the application of appropriate WHO recommended treatment options for different cyst types. Follow-up strategies have to be in place prior to the implementation of such surveys for all infected individuals who do not require treatment and for all suspected, but not confirmed, cases found during the surveys. The use of US in community screening surveys has revealed the complexity of ethical issues (informed consent, confidentiality, follow-up, detection of lesions that are not the focus of the study etc) and also provided real solutions to providing the most ethical guidelines for the early detection and treatment of CE and AE.

Assessment of a serological test for the detection of Echinococcus granulosus infection in dogs in Kenya

Specific diagnosis of Echinococcus granulosus infection in dogs has played a significant role in implementing hydatid control programs. Most programs have relied on purging dogs with arecoline hydrobromide and examining purge samples for worms to diagnose infection. This technique is time consuming and suffers from limitations including poor sensitivity, particularly in dogs with light infections, risk of hydatid infection to control personnel and severe side-effects of the arecoline in some dogs. Also, availability of praziquantel in several countries has further limited the value of the technique as owners can treat their dogs to eliminate worms prior to presenting them for purging. Application of a simple and sensitive immunological or serological detection system would overcome these problems and be a useful adjunct in control programs. Reports have described alternative techniques which show promise for accurate diagnosis of E. granulosus infection in the definitive host (Jenkins and Rickard, 1985, 1986; Craig et al., 1988). Recently, an enzyme-linked immunosorbent assay (ELISA) using E. granulosus protoscolex antigen was developed (Gasser et al., 1988), and its sensitivity was higher than the level achieved in studies using arecoline testing (Gemmell, 1968; Trejos et al., 1975). The aim of the present study was to assess the performance of the ELISA in an endemic area of Kenya for detecting dogs with E. granulosus infection, and comparing serological data with parasitological data obtained from the dogs by necropsy. Dogs shot in north-western Turkana (Oropoi, Nanam, Lokichoggio, Lakankai,

Public health education/importance and experience from the field. Educational impact of community-based ultrasound screening surveys.

The public health educational impact of community-based ultrasound (US) surveys for cystic echinococcosis (CE) can form an important part of the development about the awareness of the importance of the disease in an endemic area. In addition to identifying asymptomatic carriers and thereby facilitating early diagnosis and treatment, such surveys can be used to impart important educational messages at the individual, household, community, regional and national levels. US surveys are usually appealing to rural communities where such services are not available but where the technique is generally appreciated by its application in a wide field of medical applications. The qualities of the test (painless, non-invasive and gives instant recordable results) are also attractive to participants during such surveys and the majority of the population in a selected study area choose to be screened. Two such surveys were carried out amongst the Berber people of the mid-Atlas mountains in central Morocco in May 2000 and 2001. Over 11,000 people were screened in the two 10-day surveys. Informed consent had been obtained through community meetings and with the chiefs of villages prior to the surveys being conducted. Individuals who volunteered to be screened entered the study and as far as is known there were no refusals. The concept of voluntary participation, the explanation of the life cycle and clinical manifestations of the disease and its prevention are all-important educational messages. The occurrence of CE is almost always known in an endemic community but is usually very poorly understood leading in many cases to a fear of the disease, especially amongst families with an infected individual who has previously undergone surgery. During the US survey considerable attention was paid to provide educational input before, during and after the survey. Information was provided at the start of the survey to local leaders, doctors, veterinarians and school teachers on the aims of the study and to obtain informed consent. At the start of the study everyone was individually schooled about the route of transmission of the parasite and how this may be best prevented. The knowledge level of those screened was assessed by showing hydatid cysts, either freshly obtained from the abattoir of from photographs. Animal cysts were recognised by almost everyone but its transmission and link to human disease was invariably unknown. Patients found to be infected with CE were always confidentially counselled and followed up for treatment, if required. Treatment options were explained to the individual or to parents in the case of a child. Local physicians participated in discussions on the WHO guidelines for the treatment of CE and all cases were fully discussed providing an educational element for the local doctors. The 1% US prevalence found sent an important message to the local politicians and the perceived importance of the disease had an impact at the leadership level. Local leaders made calls for a control programme. The long term educational impact remains to be evaluated as does the role such surveys play in the future collaboration of communities with the implementation of a control programme.

Epidemiology and control of parasites in nomadic situations

Nomadism is a highly specialised mode of life that enables humans to exploit resources that are widely distributed over space and time. The isolation and remoteness of many nomad populations have limited studies on the macroepidemiology of parasitic infection in nomad populations. From the available information, the influence of a number of factors on the prevalence and transmission of parasitic infections in nomads is discussed. Environmental conditions, especially relative humidity and temperature, profoundly influence parasitic diseases. Human behaviour varies with cultural factors and influences exposure to disease. Periodic movements of nomads may either remove them and their animals from contaminated environments or may bring then into contact, often seasonally, with infections. There may be a strong ecological interdependence between diet and infection and disease in nomadic groups. Finally, the influence of drought can be profound in that seasonal or prolonged drought promotes concentration of populations in small areas or their sedenterisation, often with an increase in parasite transmission. Relevant information that needs to be acquired to develop appropriate practical and cost-effective health and veterinary care and control programmes for nomadic populations and their livestock is outlined.

The effect of transhumance on the epidemiology of animal diseases

Abstract Transhumance, the seasonal movement of people and their livestock to regions of different climate is a way of life for tens of millions of people living in the cool mountainous or the arid and semi-arid regions of the world. Transhumant peoples migrate through and spend most of the time in areas where there are invariably no veterinary, medical or educational facilities, nor abattoirs, safe water supplies or sanitation. Prevalent diseases go unrecorded and there are rarely any attempts made at disease control. The epidemiology of different diseases in transhumant communities is additionally influenced by their peculiar animal husbandry practices, the different species of livestock maintained, the close association of humans and their livestock and the small isolated groups and their frequent migrations. The frequency of these migrations will remove them from the build-up of free-living parasites including most of the faecally transmitted protozoans and helminths and also from the huge numbers of nuisance flies. Migrations, however, increase their chances of coming into contact with geographically limited or seasonally abundant diseases. In Africa, these include, Trypanosoma spp. and Cowdria ruminantium , which have a profound effect on migration patterns. Migrations also increase the opportunity for the interaction of domestic and wild animals, which facilitates the transmission of a number of shared diseases, particularly bacterial, viral, rickettsial and protozoan infections. Temperature and relative humidity play an important role in determining the distribution of those parasite species which have free-living forms or have indirect life cycles, particularly those involving invertebrate hosts. The relative importance of all the above factors on the epidemiology of different parasite species found in the cold and/or arid regions of the world occupied by transhumant peoples and their livestock is discussed.

Prevalence of human hydatid disease in northwestern Libya: a cross-sectional ultrasound study.

A total of 4103 people were screened in an ultrasound survey of the prevalence of hydatid disease (Echinococcus granulosus) in five areas of northwestern Libya; hydatid cysts were seen in 57 (1.4%), an overall prevalence of approximately 2.0% when adjusted for the likelihood of the occurrence of cysts in other sites in the body. All ultrasound-positive cases were confirmed by dot-blot ELISA. The prevalence of hydatid cysts increased with age, and differed between the sexes except in the five to 14 age group. All diagnosed cases, even those with large cysts, were asymptomatic. This study demonstrates the value of ultrasonography for screening field populations for hydatid disease. The technique was well received locally, facilitating the rapid collection of prevalence data from all ages and both sexes. Libyan people keep guard dogs, but there is little direct human:dog contact. Many people own a single dog, invariably kept outside and often chained up. Stray dogs are common, roaming the countryside to scavenge sheep carcases etc., and such dogs could be the main reservoir of E. granulosus in Libya. Because of the minimal direct human:dog contact, transmission of hydatid disease in Libya is probably indirect by ingestion of eggs from contaminated vegetables or drinking water.